Sensor, circuitry, and method for wireless intracranial pressure monitoring

ABSTRACT

An intracranial pressure monitoring device includes a housing defining a first internal chamber, a plurality of strain gauges disposed on an inner surface of a diaphragm defined by a wall of the first internal chamber, a device for generating orientation signals, and circuitry coupled to the plurality of strain gauges and to the device. The circuitry is configured to generate intracranial pressure data from signals received from the plurality of strain gauges, generate orientation data based on the orientation signals received from the device, and store the intracranial pressure data and the orientation data in a computer readable storage such that the intracranial pressure data and orientation data are associated with each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application No.61/475,216 filed on Apr. 13, 2011, the entirety of which is hereinincorporated by reference.

BACKGROUND

The disclosed systems and methods relate to extradural pressure monitorsfor monitoring and storing values related to intracranial pressure. Thedisclosed devices can be implanted in a head of a patient for eithershort- or long-term monitoring. The transmission of stored or real-timedata to an external device consists of a radio-frequency communicationcircuit in the device.

Intracranial pressure rises in the settings of a number of acute insultsto the brain including trauma, stroke, swelling, hemorrhage, andhydrocephalus. Currently there does not exist a wireless device thatmeasures intracranial pressures reliably and safely. Such a device wouldimprove monitoring in the hospital setting and would furthermore enableintracranial pressure monitoring in the outpatient setting.

Existing intracranial pressure (“ICP”) monitoring devices havesignificant shortcomings which make them impractical for stable andaccurate monitoring of intracranial pressure for the long term. Mostdesigns involve either externalization of a fluid column or tunneling awire connection to an external monitor. As such methods leave an opentract between the external environment and the brain, the likelihood ofinfection is high.

Additionally, existing ICP devices have significant technicalshortcomings. For example, many ICP devices are centered around gaugeshaving a capacitance that varies with pressure, which are measured orsensed by LC circuits having a resonance that varies with thiscapacitance change. This approach, however, typically suffers from agreat deal of drift in the gage readings.

Some designs involve measuring volume changes in a fixed amount of atrapped fluid, which, lacking adequate temperature compensation, makethe device's readings subject to both bodily and environmentaltemperature changes. Additionally, previous designs' methods oftransmitting data have been insufficient, as they have been slow, noisy,and inconsistent.

SUMMARY

An intracranial pressure monitoring device includes a housing defining afirst internal chamber, a plurality of strain gauges disposed on aninner surface of a diaphragm defined by a wall of the first internalchamber, a device for generating orientation signals, and circuitrycoupled to the plurality of strain gauges and to the device. Thecircuitry is configured to generate intracranial pressure data fromsignals received from the plurality of strain gauges, generateorientation data based on the orientation signals received from thedevice, and store the intracranial pressure data and the orientationdata in a computer readable storage such that the intracranial pressuredata and orientation data are associated with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front isometric view of one example of an intracranialpressure monitoring device.

FIG. 2 is a cross-sectional view of the intracranial pressure monitoringdevice illustrated in FIG. 1.

FIG. 3 is a cross-sectional view of the proximal portion of theintracranial pressure monitoring device illustrated in FIG. 1.

FIG. 4 is a cross-sectional view of the distal portion of theintracranial pressure monitoring device illustrated in FIG. 1.

FIG. 5 is a bottom-side plan view of one example of an intracranialpressure monitoring device in accordance with some embodiments.

FIG. 6A illustrates one example of a layout of strain gauges disposed onthe sensing diaphragm of an improved intracranial pressure monitoringdevice.

FIG. 6B illustrates an example stress plot indicating locations ofneutral axes for the diaphragm in FIG. 6A.

FIG. 7 illustrates one example of the electrical connections of thesensors illustrated in FIG. 6A.

FIG. 8 illustrates one example of a printed circuit board and thecircuitry disposed on the printed circuit board in accordance with theintracranial pressure monitoring device illustrated in FIG. 1.

FIGS. 9A-9D are various views of another example of an intracranialpressure monitoring device.

FIG. 10 is a cross-sectional view of the intracranial pressuremonitoring device illustrated in FIGS. 9A-9D.

FIG. 11 illustrates one example of a circular printed circuit board andthe circuitry disposed on the circular printed circuit board inaccordance with the intracranial pressure monitoring device illustratedin FIGS. 9A-9D.

FIG. 12A illustrates various places on a human skull at which theintracranial pressure monitoring devices may be positioned.

FIG. 12B is a cross-sectional view of an intracranial pressuremonitoring device installed within a skull of a patient.

FIG. 13 illustrates an example ICP waveform of processed digitizedvoltages of signals from strain gauges.

FIG. 14 is an isometric view of one example of a hand-held external unitconfigured to transmit data to and receive data from an intracranialpressure monitoring device in accordance with FIGS. 1 and 9A-9D.

FIG. 15 illustrates an example of an external unit configured totransmit data to and receive data from an intracranial pressuremonitoring device in accordance with FIGS. 1 and 9A-9D.

FIG. 16 illustrates an example of an external unit configured totransmit data to and receive data from an intracranial pressuremonitoring device in accordance with FIGS. 1 and 9A-9D.

FIG. 17 illustrates an example of an external unit configured totransmit data to and receive data from an intracranial pressuremonitoring device in accordance with FIGS. 1 and 9A-9D.

FIG. 18 illustrates one example of a network-based patient monitoringsystem.

FIG. 19 is a flow diagram of one example of a method of calibrating anICP monitoring device in accordance with some embodiments.

FIG. 20 is a flow diagram of one example of monitoring performed by anICP monitoring device in accordance with some embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The disclosed intracranial pressure (“ICP”) monitoring devices andmethods advantageously enable the short- or long-term monitoring andstorage of ICP data in an implanted monitor capable of transmitting thisdata to an external reader. The disclosed devices have improved driftcharacteristics and lower infection risks. The disclosed devices andmethods enable performing statistical signal analysis on the measuredICP data for purposes of assisting the clinical diagnosis. The dataacquired by the device can be transmitted via a fast, reliable, radiofrequency communication circuit.

The disclosed devices include low drift, matched semiconductor straingauges, which transduce deflection in the sensing portion of the device.In some embodiments, the sensing portion of the device is a fixed-edgeextended-ridge diaphragm constructed in such a way as to cause thestrain in the diaphragm at the location of the ends of the strain gagesto be optimal for their drift characteristics.

In some embodiments, the devices are powered by a mechanism, such as abattery, by an inductive coil in combination with a capacitor, or both,which allows for maximum flexibility of operation. The device alsoconserves power by putting the microprocessor and peripheral electronicsinto low-power modes between measurements, reducing their overall powerdraw.

FIG. 1 illustrates one example of an ICP monitoring device 100-1includes a housing 102 extending from a distal end 104 to a proximal end106. In some embodiments, housing 102 has a circular cross-sectionalarea as best seen in FIGS. 1, 5 and 6 and is formed from a metal suchas, for example, titanium, stainless steel, gold, silver, or otherbiocompatible metal. Although housing 102 of ICP monitoring device 100-1is described as having a circular cross-sectional geometry, one ofordinary skill in the art will understand that housing 102 may haveother geometries.

As shown in FIGS. 1-3, a portion of the exterior surface 108 of housing102 includes self-tapping threads 110 for securing ICP monitoring device100 to the skull of a patient. In some embodiments, such as the bottomside view illustrated in FIG. 5, the exterior surface 108 of housing 102does not include threads and is instead coupled to the skull of apatient via a press fit and/or through the use of one or more outwardlyextending tabs 103-1, 103-2, 103-3, 103-4 (collectively “tabs 103”) eachdefining a respective hole 105-1, 105-2, 105-3, 105-4 (collectively“holes 105”) for receiving a screw, which is used for securement.Although four tabs 103 and holes 105 are illustrated in FIG. 5, one ofordinary skill in the art will understand that the number of tabs 103and holes 105 may be greater than or less than four.

Housing 102 defines an internal chamber 112 (FIG. 2) in which a printedcircuit board (“PCB”) 114 is disposed. In some embodiments, such as theembodiment illustrated in FIG. 2, housing 102 includes a proximalcomponent 116 that is coupled to a distal component 118. As shown inFIGS. 2 and 3, proximal component 116 includes a chamber sealing wall120 from which a circular side wall 122 extends in a first direction.

Distal component 118, which is best seen in FIGS. 2 and 4, includes abottom wall 124, which defines a fixed-edge diaphragm as described ingreater detail below, from which circular side wall 126 extends.

Proximal component 116 and distal component 118 are coupled together toprovide a hermetic seal such that chamber 112 has an internal pressure,which is known. In some embodiments, chamber 112 has a pressure that islower than all anticipated pressures expected to be exerted on bottomwall 124 during normal operating conditions when ICP monitoring device100-1 is implanted in a skull of a patient. Sealing chamber 112 at aknown pressure that is lower than expected operating pressures mitigatesthe possibility of an effect known to those of ordinary skill in the artas “oil-canning,” in which a transition from concave to convexconformations, or vice versa, induces erroneous gauge readings andsignal noise.

In some embodiments, chamber 112 is filled during manufacturing with agas such as Argon, Helium, or other combination of gases. In someembodiments, chamber 112 is filled with an electrically insulatingliquid or is evacuated prior to sealing. The effect of controlling thecontents of the sealed chamber 112 is to create a reference pressureagainst which the degree of deformation of the fixed-edge diaphragm maybe measured in order to correlate to an external pressure experienced bythe diaphragm. Controlling the contents of sealed chamber 112 alsocontrols and defines the characteristic pressure changes in the chambercontents, which affects the gauges and pressure readings as thetemperature changes.

In some embodiments, the internal surface 128 of side wall 122 ofproximal component 116 defines one or more threads 130 that areconfigured to engage one or more threads 132 disposed on the externalsurface 134 of side wall 126 of distal component 118. In someembodiments, threads 132 are formed on a first portion 136 of side wall126 that is less than an entire length of side wall 126 such thatportion 138 is unthreaded. Portion 138 is left unthreaded to isolatefixed-edge diaphragm 124 from heat and stress concentrations inducedduring the threading process.

Bottom wall 124, which defines the fixed-edge diaphragm, comprises animpermeable, sealed diaphragm that is configured to interface with thedural sac, pial layer, brain parenchyma, or cerebro spinal fluid asdescribed below. A ridge 140 extends between and forms the interfacebetween side wall 126 and bottom wall 124. Ridge 140 extends at anon-perpendicular angle with respect to side wall 126 and bottom wall124 to change the stress concentrations as described below. In someembodiments, the thickness of bottom wall 124 is between 0.004 inchesand 0.005 inches, although one of ordinary skill in the art willunderstand that bottom wall 124 may have other thicknesses. Thethickness of side wall 126 may be varied although it should besufficiently thick to withstand stresses from manufacturing and inducedstress from being under pressure in situ.

In some embodiments, the external surface 142 of bottom wall 124, whichforms the diaphragm, is electro-polished or coated with materials ordrugs known to prevent scar tissue overgrowth. Fibrous tissue overgrowthoccurs within several weeks of implantation of foreign material into thebody. While the formation of scar tissue overgrowth is a normal part ofthe body's physiological healing response, it is typically undesirableas it can affect pressure transmission across diaphragm 124.Additionally, contraction of such scar tissue can artificially deform orgenerate pressures on the diaphragm. Examples of materials that may bedeposited on external surface 142 include, but are not limited to,polyvinylpyrrolidone (“PVP”), phosphoryl colene, polyethylene oxide(“PEO”), hydro-gels, and paralene, to name a few possible materials.Examples of drugs that may be disposed on the external surface 142 ofbottom wall 124 includes, but are not limited to, anti-inflammatoryagents, cell cycle inhibitors, anti-platelet agents, anti-thrombincompounds, and thrombolytic agents.

External surface 142 is fabricated to provide a flat surface. As will beunderstood by one of ordinary skill in the art, a flatter diaphragm 124is less compliant and thus the electrical changes induced in gauges 146mounted on the diaphragm 124 will have a higher gain than from a lessflat diaphragm. Thus, a flat diaphragm minimizes the dampening effectsof tissue overgrowth by enabling more sensitive gauge measurements.

The internal surface 144 of bottom wall 124 may support one or morestrain gauges 146-1, 146-2, 146-3, and 146-4 (“strain gauges 146”).Strain gauges 146 may be connected to bottom wall 124 using an epoxy orother securement material or means. In some embodiments, such as theembodiment illustrated in FIG. 6A, four strain gauges are implementedwith one pair of strain gauges 146-2, 146-3 being aligned in parallelnear the center 148 of bottom wall 124 and the other pair of straingauges 146-1, 146-4 are disposed in parallel with one another adjacentto one another and perpendicular to gauges 146-2, 146-3. Put anotherway, parallel gauges 146-1 and 146-4 are disposed farther way fromcenter 148 than gauges 146-2 and 146-3, which are disposed perpendicularto gauges 146-1 and 146-4.

The center 148 of diaphragm 124 experiences a higher tangential straincompared to the outer edge 140, which experiences a higher radial strainof opposite polarity. The particular placement of these gauges 146 onso-called “axes of neutrality,” which refer to regions 150-1, 150-2 ondiaphragm 124 where compression and tension are close to zero. Suchminimization of net forces is created by extending the angle or ridge140. This technique is designed to minimize mechanical deformations inthe affixing substance. Such placement of gauges 146 increases thestability and lifespan of the gauges 146 as the strain and resultingdeformation experienced by the epoxy affixing gauges 146 to diaphragm124 is minimized.

For example, potential drift of resistive-based pressure sensors comesfrom a number of sources that alter the physical properties of the gauge146, which causes net electrical characteristics of the gauge elements146, e.g., resistance, to change in an unpredictable fashion. Thesesources include deterioration of the gauges, warping or fatigue of thesensor, and a gradual breakdown of the adhesive used to attach thegauges to the sensor. An extended ridge diaphragm advantageously allowsfor the ends of the semiconductor strain gauges 146 to be placed alongtwo neutral axes where zero strain, or close to zero strain, isexperienced. A neutral axis arises at transition point from compressiveto tensile stress as shown in FIG. 6B. By extending a peripheral ridge140 upon the outside edge of the diaphragm 124 (approximately 1/10th theradius of the diaphragm), the diaphragm 124 effectively includes twoneutral axes where strain is negligible as shown in FIG. 6B. Placing theends of the semiconductor gauges 146 along the two neutral axes providesenhanced stability and durability.

In some embodiments, the two radial strain gauges 146-1, 146-4 areoriented 90 degrees from each other instead of 180 degrees asillustrated in FIG. 6A. Such arrangement results in partial cancellationof forces induced on the sides of the diaphragm 124.

The thickness of the epoxy used to attach gauges 146 to diaphragm 124can be minimized to reduce the amount of viscoelastic drift causedduring normal usage, particularly when a constantly elevated pressure isexerted on the diaphragm as in the human body. To support theminimization of thickness of epoxy used, a silicon dioxide or otherinsulating layer is grown on the bottom of the strain gauges 146 or oninner surface 144 of diaphragm 124 such that the adhesive employed neednot be thick enough to serve as the only insulating element.

In some embodiments, such as the embodiment illustrated in FIG. 2,strain gauges 146 are coupled to contact blocks 152, which may bedisposed on interior surface 154 of side wall 126 of distal component118. The coupling between strain gauges 146 and contact block 152 isprovided by wires 156. Wires 156 also connect contact block 152 to PCB114 as illustrated in FIG. 2. In some embodiments, contact block 152 isomitted and wires directly connect strain gauges 146 to PCB 114.

Strain gauges 146 are electrically connected to form a full Wheatstonebridge 158 as illustrated in FIG. 7. In particular, strain gauge 146-1is coupled to strain gauge 146-2 at node 160, which serves as a firstoutput node of Wheatstone bridge 158. Strain gauge 146-1 is also coupledto strain gauge 146-3 at node 162, which receives a positive voltagefrom a first voltage source 164 through resistor 166. Strain gauge 146-3is coupled to strain gauge 146-4 at node 168, which serves as a secondoutput node for Wheatstone bridge 158. Strain gauges 146-4 and 146-2 arecoupled together at node 170, which is coupled to a low voltage powersupply such as ground. However, one of ordinary skill in the art willunderstand that nodes 162 and 170 may be coupled to other supplyvoltages and that positive and negative do not necessarily have aphysiological meaning in connection with ICP.

FIG. 8 illustrates some of the circuitry that may be formed on PCB 114.The circuitry formed on PCB 114 may include discrete components and/orbe formed in an integrated circuit (“IC”) or packaged together as anapplication specific integrated circuit (“ASIC”). As shown in FIG. 8, alow-drift differential amplifier 172 receives signals from nodes 160 and168 of Wheatstone bridge 158 and outputs a signal to a microprocessor174, which is configured with an analog-to-digital converter (“ADC”). Insome embodiments, the ADC is a discrete component separated frommicroprocessor 174. Microprocessor 174 is in signal communication with anon-transient computer readable storage medium 176, such as a randomaccess memory (“RAM”), a flash memory, or other storage device, and witha communication module 178 configured for radio frequency (“RF”)communication or communication using other frequencies.

RF communication module 178 is coupled to an antenna 180 configured totransmit and receive wireless signals. In some embodiments,communication module 178 is configured to communicate using Bluetooth,Near-Field Communication, or other communication protocol for near ordistant communication. In some embodiments, communication module 178 isa transceiver configured to transmit and receive signals in anunregulated band, such as the 2.4 GHz frequency band. One of ordinaryskill in the art will understand that other communication protocols andtransmission frequencies may be used.

Additional circuitry may also be disposed on PCB 114 for enhanced datagathering. In some embodiments, for example, a gyroscope 182, anaccelerometer 184, both, or another device for determining anorientation of ICP monitoring device 100 relative to a verticaldirection or axis are disposed on PCB 114. The gyroscope and/oraccelerometer may be single- or multi-axis devices manufactured usingMEMS technology. These devices 182, 184 are utilized to determine theorientation of the patient's head, which affects the measured ICP aswill be understood by one of ordinary skill in the art. For example, apatient's ICP will be higher when supine, e.g., perpendicular to thevertical direction or axis, than when sitting upright (e.g., parallel tothe vertical direction or axis), due to the effect of gravity on thepatient's cerebral spinal fluid (“CSF”).

In some embodiments, gyroscope 182 and/or accelerometer 184 areconfigured for use in long-term sensor implantation scenarios to monitora patient's orientation. For example, devices 182 and 184 can be used todetect a patient falling and cause microprocessor 174 to record the timeof the fall for later correlation with a rise in ICP. In someembodiments, the detection of a fall will trigger an alert to thepatient, primary caregiver, or emergency services based on a rise in ICPassociated with a fall. Patient orientation is also useful indetermining and recording when the patient is awake or asleep. Forexample, diagnostic measurements for normal pressure hydrocephalus aretypically obtained when a patient is sleeping. Microprocessor 174 can beprogrammed to obtain such measurements when gyroscope 182 and/oraccelerometer 184 provide signals to microprocessor 184 identifying thatthe patient is lying down. In some embodiments, such measurements areonly recorded after it is determined the patient has been lying down fora period of time that exceeds a threshold, e.g., 10 minutes, 20 minutes,etc.

The electronics disposed on one or more PCBs 114 are powered by a powersupply 186. In some embodiments, power supply 186 includes a batterywhile in other embodiments the electronics are powered by another powersupply. For example, the electronics disposed on PCB 114 can receivepower via inductive coupling between a coil antenna 188 in or on top ofthe implant and another coil antenna in or outside of an external unitas described in greater detail below. Each of these coil antennas makeup a portion of a resonant circuit that includes inductors, capacitors,and resistors such that the circuit is electrically resonant at apredetermined frequency. A powered resonant circuit brought into thevicinity of a circuit resonant at a close frequency or a harmonic willinductively couple with the second circuit thereby inducing a current toflow. This current can be used to run the implanted electronics orcharge a capacitor of power supply 186 that stores energy for poweringthe electronics disposed on PCB 114.

Another embodiment of an improved ICP monitoring device 100-2illustrated in FIGS. 8A-8D, which provide various views of device 100-2.As illustrated in FIGS. 8A-8D, ICP monitoring device 100-2 includes ahousing 102 extending from a distal end 104 to a proximal end 106. Insome embodiments, housing 102 has a circular cross-sectional area asbest seen in FIGS. 8C and 8D and is formed from a metal such as, forexample, titanium, stainless steel, gold, silver, or other biocompatiblemetal.

As best seen in FIGS. 8A, 8B, and 8D, the exterior surface 108 ofproximal portion 116 of housing 102 includes self-tapping threads 110for securing ICP monitoring device 100-2 to the skull of a patient.Distal portion 118 of housing 102 includes a smooth outer surface 134having an outer diameter that is smaller than an outer diameter ofproximal portion 116 enabling distal portion 118 to pass through theinner dimension of the ridge of bone created by an anti-plunge cranialperforator as will be understood by one of ordinary skill in the art. Insome embodiments, housing 102 and the burr hole created by such drillingmechanism are complementary such that CSF is prevented from leakingthrough the burr hole around housing 102.

In some embodiments, a circumferential trough 135 is formed along thelength of distal portion 118 as can be seen in FIGS. 8A, 8B, and 8D.Trough 135 advantageously isolates fixed-edge extended-ridge diaphragm124 and strain gauges 146 from stresses and strains afflicted on thehousing during implantation. Such stresses and strains can deformdiaphragm 124 and cause damage or measurement drift.

Turning now to FIG. 10, it can be seen that distal portion 118 ofhousing 102 defines an internal chamber 112 in which strain gauges146-1, 146-2, 146-3, and 146-4 are disposed. As described above, straingauges 146 are affixed to bottom wall 124, which forms the fixed-edgediaphragm, by epoxy or other means. As described above with respect toFIG. 6A, strain gauges 146 can be disposed on bottom wall 124 such thatstrain gauges 146-2, 146-3 are aligned in parallel with one another nearthe center of bottom wall 124 and the other pair of strain gauges 146-1,146-4 are disposed in parallel with one another adjacent to one anotherand perpendicular to gauges 146-2, 146-3. Extended ridge 140 extends ata non-perpendicular angle with respect to side wall 126 and bottom wall124 to change the stress concentrations as described above.

The thickness of the epoxy used to attach gauges 146 to diaphragm 124can be minimized to reduce the amount of viscoelastic drift due tolong-term variations in average pressure, due to, for example, a patienttraveling to a higher or lower altitude. To support the minimization ofthickness of epoxy used, a silicon dioxide or other insulating layer isgrown on the bottom of the strain gauges 146 or on inner surface 144 ofdiaphragm 124 such that the adhesive employed need not be thick enoughto serve as the only insulating element. Side wall 126 extends frombottom wall 124 to interface 117 where distal portion 118 is joined toproximal portion 116.

Proximal portion 116 defines a recessed area 119 that houses PCB 114 onwhich the electronics are disposed. Silicon potting or otherbiocompatible material disposed in recessed area 119 over PCB 114 andthe electronics disposed thereon. The shape formed by the potting isdesigned to minimize the potential for skin necrosis around theimplant's external proximal end. Placing PCB 114 and the electronics inrecessed area 119 reduces the interference of the housing material onthe function of the electronics, particularly the coil antenna.

Proximal portion 116 also defines an engagement feature 121 that isconfigured to receive or engage a tool for aiding in insertion of ICPmonitoring device 100-2 into a skull of a patient. In some embodiments,engagement feature 121 is configured to receive a tool having ahexagonal cross-sectional area, although one of ordinary skill in theart will understand that engagement feature 121 may be complementary totools having other cross-sectional geometries including, but not limitedto, stars and squares.

In some embodiments, proximal portion 116 and distal portion 118 areformed from a single piece of a rod. In some embodiments, proximalportion 116 and distal portion 118 are coupled together at interface 117by laser welding or screw threads. In some embodiments, a ceramicfeed-through is brazed to side wall 126 and to proximal portion 116 tojoin proximal portion 116 to distal portion 118 at interface 117 and toallow wires 156 to pass from chamber 112 defined by distal portion 118to recessed area 119 defined by proximal portion 116.

Proximal portion 116 and distal portion 118 are coupled together toprovide a hermetic seal such that chamber 112 has a known internalpressure. As described above, chamber 112 can be filled duringmanufacturing with a gas such as Argon, Helium, or other combination ofgases. In some embodiments, chamber 112 is filled with an electricallyinsulating liquid or is evacuated prior to sealing. The effect ofcontrolling the contents of the sealed chamber 112 is to create areference pressure against which the degree of deformation of thefixed-edge diaphragm may be measured in order to correlate to anexternal pressure experienced by the diaphragm 124. As described above,controlling the contents of sealed chamber 112 also controls and definesthe characteristic pressure changes in the chamber contents, whichaffects the gauges and pressure readings as the temperature changes.

In some embodiments, the external surface 142 of bottom wall 124, whichforms the diaphragm, is electro-polished or coated with materials ordrugs known to prevent scar tissue overgrowth. Fibrous tissue overgrowthoccurs within several weeks of implantation of foreign material into thebody. Examples of materials that may be deposited on external surface142 include, but are not limited to, polyvinylpyrrolidone (“PVP”),phosphoryl colene, polyethylene oxide (“PEO”), hydro-gels, and paralene,to name a few possible materials. Examples of drugs that may be disposedon the external surface 142 of bottom wall 124 includes, but are notlimited to, anti-inflammatory agents, cell cycle inhibitors,anti-platelet agents, anti-thrombin compounds, and thrombolytic agents.

External surface 142 is fabricated to provide a surface that is as flatas possible. As described above, a flatter diaphragm 124 is lesscompliant and thus the electrical changes induced in gauges 146 mountedon the diaphragm 124 will have a higher gain than from a less flatdiaphragm. Thus, a flat diaphragm minimizes the dampening effects oftissue overgrowth by enabling more sensitive gauge measurements.

Strain gauges 146 are coupled to PCB 114 via wires 156 and areelectrically connected to form a full Wheatstone bridge 158 asillustrated in FIG. 7. FIG. 11 illustrates one example of a circular PCB114 having a circular cutout 115. PCB is sized and configured to bereceived within recess 119 on which circuitry is formed. Locating PCB114 in recess 119 isolates the electronics disposed on PCB 114 fromchamber 112 to mitigate the effects of the housing 102 on the inductivecoupling between housing 102, antenna 180, and coil 188.

As shown in FIG. 11, a low-drift differential amplifier 172 receivessignals from nodes 160 and 168 of Wheatstone bridge 158 and outputs asignal to a microprocessor 174, which is configured with an ADC.Microprocessor 174 is in signal communication with a non-transientcomputer readable storage medium 176, such as a RAM, a flash memory, orother storage device, and with a communication module 178 configured forwireless communication. Other circuitry for performing analog/digitalfiltering, analog/digital smoothing, frequency analysis, and time domainoperations can be disposed on PCB 114.

RF communication module 178 is coupled to an antenna 180 configured totransmit and receive wireless signals. In some embodiments,communication module 178 is configured to communicate using Bluetooth,Near-Field Communication, or other communication protocol for near ordistant communication. In some embodiments, communication module 178 isa transceiver configured to transmit and receive signals in anunregulated band, such as the 2.4 GHz frequency band. One of ordinaryskill in the art will understand that other communication protocols andtransmission frequencies may be used.

A gyroscope 182 and/or an accelerometer 184 are disposed on PCB 114. Thegyroscope and/or accelerometer may be single- or multi-axis devicesmanufactured using MEMS technology. These devices 182, 184 are utilizedto determine the orientation of the patient's head, which affects themeasured ICP as will be understood by one of ordinary skill in the art.For example, a patient's ICP will be higher when supine than whensitting upright or standing upright, due to the effect of gravity on thepatient's CSF.

Additionally, gyroscope 182 and/or accelerometer 184 disposed on PCB 114may be utilized to determine and/or identify medically relevant eventssuch as, for example, a patient falling. Devices 182, 184 can be used torecord the force with which the fall impacted the patient's skull and becorrelated with changes in ICP before, during, and/or after the event todetermine various causes and effects of the event as well as aid inmedical diagnosis and/or treatment.

The improved ICP monitoring devices 100-1, 100-2 (“ICP monitoringdevices 100”) described above may be installed at various locations inthe skull 10 of a patient. In some embodiments, an ICP monitoring device100 is installed at Frazier's Point 12 or in Kocher's Point 14 in askull as illustrated in FIG. 12A. The method of installing an ICPmonitoring device 100 in a skull 10 of a patient is described withreference to FIGS. 12A and 12B.

The skin 20 and fascia 22 are removed from the insertion side to exposethe patient's skull 10 as best seen in FIG. 12B. As described above, theinsertion site may be at the Frazier's Point 12 located 3 cm lateral tothe midline and 6 cm superior to the inion, the Kocher's Point 14located 11 cm posterior to the nasion and 2.5 cm lateral to midline, orat another location as will be understood by one of ordinary skill inthe art. For example, ICP monitoring device 100 both above or below thetentorium at locations commonly used positions for placement ofintraventricular catheters.

A cranial burr hole is made in a patient's skull 10 by a surgeon usingan anti-plunge cranial perforator, a drill, or other tool. The hole ismade by the surgeon to expose the dural sac 24 surrounding the brain 26of the patient.

An ICP monitoring device 100 is then inserted into the hole formed inthe skull 10 as illustrated in FIG. 12B. In some embodiments, housing102 is threaded into skull bone 10 such that self-tapping threads 110dig into skull bone 10 as ICP monitoring device 100 is rotated. Inembodiments when the cranial burr hole has an irregular shape, e.g.,non-circular shape, an adapter grommet (not shown) defining a centralpassageway sized and configured to receive ICP monitoring device 100 isfirst inserted to cranial burr hole. The adapter grommet may have across-sectional area that is complementary to the cranial burr holeformed in the patient's skull 10.

In some embodiments in which housing 102 does not include threads 110,i.e., the outer surface 108 of housing is smooth, proximal portion 116may have an outer diameter that is greater than a diameter of cranialburr hole such that distal portion 118 is received within the hole andproximal portion 116 abuts the outer surface of skull bone 10. Tabs 103(FIG. 5) may outwardly extend from proximal portion 116 and each definean opening 105 sized and configured to receive screws that assist inaffixing ICP monitoring device 100 to skull 10.

The depth to which ICP monitoring device 100 is installed may be varied.For example, ICP monitoring device 100 is installed such that diaphragm124 is disposed flush with or slightly below the inner table of theskull such that diaphragm 124 contacts dura 24.

In some embodiments, diaphragm 124 is positioned below a fenestrateddural layer such that diaphragm 124 is in contact with the pial layer orbrain parenchyma tissue. Such positioning may provide for improvedsensitivity to monitoring as well as reducing and/or eliminatingimpedance due to the dura matter. A surgeon may be notified that ICPmonitoring device is properly positioned by device 100 generating asignal from gauges 146 in response to diaphragm 124 contacting dura 24.The signal may be received by an external unit (described below), whichsignals the surgeon installing monitoring device 100 by emitting anaudio and/or visual indication.

Monitoring device 100 can also collect data during the installationprocess concerning stress and strain on side wall 126. For example,strain gauges 146 can generate signals identifying detected strain onhousing 124 while the ICP monitoring device 100 is being twisted intoskull 10. In such a configuration, ICP monitoring device 100 can alertthe surgeon if excessive strain is detected. Excessive strain duringimplantation may be a marker of improper implantation and may lead toinaccurate pressure readings due to diaphragm deformation.

Once the ICP monitoring device 100 is installed, initial measures can beused to calibrate the device as will be described with reference to FIG.19. As shown in FIG. 19, an ICP monitoring device 100 is implanted in apatient at block 1902. At block 1904, a pressure reading is taken andassessed to determine the quality of the contact of ICP monitoringdevice 100 and the intracranial pressure region. The pressure readingtaken by ICP monitoring device 100 may be transmitted to an externaldevice, such as an external device 300, 400, 500 described in greaterdetail below, such that a user may be able to assess the quality of theimplant.

At block 1906, a decision is made as to whether ICP monitoring device100 has been properly implanted. In some embodiments, an external devicemay display a graphical representation of an ICP waveform to a user on adisplay such that the user may assess whether or not the ICP monitoringdevice is properly implanted. In some embodiments, ICP monitoring deviceis placed in a mode in which it assesses the pressure signals todetermine whether implantation has been properly made. For example,processor 174 of ICP monitoring device receives the sensed signals fromstrain gauges 146 and determine a peak-to-peak signal voltage todetermine whether sufficient contact has been made between diaphragm 124and the intracranial surface of a patient. If it is determined thatimplantation was not successful, e.g., the contact between diaphragm 124and the intracranial pressure surface of a patient is not sufficient todetect pressure accurately, then the implantation procedure at block1902 is performed again.

If it is determined that sufficient contact has been made betweendiaphragm 124 of ICP monitoring device 100 and an intracranial surfaceof a patient, then method 1900 proceeds to block 1908 where a pluralityof calibration readings are recorded at different elevations. Forexample, the patient can be positioned in a supine position with theirhead flat, which may be recorded as a zero degree elevation. In such aposition, ICP monitoring device 100 stores the pressure waveform for apredetermined period of time as well as a position measurement thatcorresponds to signals received from gyroscope 182 and/or accelerometer184. Subsequently, the patient can be elevated to 30 degrees, 60degrees, 90 degrees, and other positions and ICP monitor 100 can recordthe pressure waveform for the predetermined period of time along withthe values measured by gyroscope 182 and/or accelerometer 184 associatedwith this position.

Alternatively or additionally, the patient can be positioned in acompletely upright, or standing, position and ICP monitoring device 100can record the waveforms received from strain gauges 146 along with thevalues measured by gyroscope 182 in these positions. As will beunderstood by one of ordinary skill in the art, processor 174 may readvalues from gyroscope 182 and store the values in non-transient computerreadable storage 176.

At block 1910, ICP values are calculated for each of the differentpositions at which the patient was positioned. The ICP values arecalculated based on the stored waveforms and are recorded with theposition data.

At decision block 1912, the calculated ICP value is compared to ameasured ICP value to determine if ICP monitoring device has beencalibrated. For example, if the calculated ICP value is not equal to themeasured ICP value, then ICP monitoring device 100 is not calibrated. Ifthe ICP value is equal to the measured ICP value, then ICP monitoringdevice 100 is calibrated and method 1900 is finished at block 1922.

If ICP monitoring device 100 is not calibrated, then method 1900proceeds to block 1914 where a lumbar drain is inserted into patient. Aswill be understood by one of ordinary skill in the art, a lumbar drainis typically a flexible, soft plastic tube that is inserted into thelower back of a patient to remove CSF. The tube can be coupled to adrainage bag for capturing the removed CSF.

At block 1916, the pressure is transduced with a patient in a zerodegree position. The lumbar drain is coupled to a pressure transducerthat is calibrated to zero at the level of the patient's tragus, whichis used as the common reference point by physicians for ICP monitoring.

At block 1918, the pressure is transduced with a patient undergoing aValsalva maneuver. The Valsalva maneuver can be performed in variousways. One way is to have the patient close his/her airway, e.g., closinghis/her mouth and pinching his/her nose closed, and trying to exhale toincrease intrathoracic pressure. In this method, the patient can exhaleagainst a pressure recording device such as a manometer, which canrecord the intrathoracic pressure. Another way to induce a Valsalva isto have the patient bear down as if having a bowel movement. TheValsalva maneuver increases intrathoracic pressure, thereby decreasingvenous outflow from the brain and increasing intracranial pressure.Performing Valsalva maneuvers while the patient is supine allows formeasurement of a range of intracranial pressures and waveforms with eachValsalva.

At block 1920, conversion parameters are adjusted based on therecalibration procedures performed at blocks 1916 and 1918. Suchadjustable parameters include, but are not limited to, the raw voltagereading of the Wheatstone bridge 158 when the patient is at variouselevations, a calculated line or curve of best fit between variousWheatstone bridge voltage readings, the raw voltage reading of thegyroscope 182 or accelerometer 184 at various elevations (to accountfor, e.g., implantation that is not perfectly level), and variouscalculated waveform parameters at various patient elevations asdescribed below. Once the adjustments have been made and ICP monitoringdevice 100 is calibrated, method 1900 moves to block 1922 and thecalibration is concluded.

Recording the measured values when the patient is disposed in knownpositions provides ICP monitoring device 100 with the ability tominimize the drift of gyroscope readings and maximizing the accuracy ofpatient position estimation, which leads to improved internal pressuremeasurements and calibration. Although calibration method 1900 isdescribed as being performed when ICP monitoring device has beenimplanted, one of ordinary skill in the art will understand that thecalibration can be conducted while the sensing diaphragm is exposed toair prior to implantation or when ICP monitoring device 100 is disposedwithin a shallow depth of fluid.

The calibrated ICP monitoring device 100 is configured to sense andstore data concerning intracranial pressure as detected by strain gauges146. As will be understood by one of ordinary skill in a measure ofpressure can be derived from a computed correlative relationship betweensensor-measured pressure and a number of waveform features. Acorrelative relationship can include any relationship, such as aformula, a graph, a curve, a linear relationship, a non-linearrelationship, a neural network, a classifier, or any other relationshipthat provides a value of one variable when presented with a value ofanother variable or variables.

The processing of the signals received from strain gauges 124 isdescribed with reference to FIG. 20. Mechanical strains on diaphragm 124are sensed by strain gauges 146, which generate electrical analogsignals in response. These analog signals are digitized at block 2002 byan ADC, such as an ADC of processor 174 or a separate ADC.

At block 2004, the digitized voltage are processed to generate an ICPwaveform, such as the ICP waveform illustrated in FIG. 13. In someembodiments, the digitized voltages are converted to a characterizedwaveform in a fixed method, and in some embodiments, the digitizedvoltages are converted to a characterized waveform in a dynamic methodas will be understood by one of ordinary skill in the art. As shown inFIG. 13, the ICP waveform includes three peaks (P1, P2, P3).

At block 2006, an ICP value is calculated based on the waveform using alinear, quadratic, or other approximation method. The values derivedfrom the waveform features can be selected from a group of parametersfor each peak including amplitude, rate of ascent, and rate of descent,among others. Additionally, timing of any of the aforementioned waveformfeatures can be taken with respect to the cardiac or respiratory cycleor timing of another ICP waveform feature. A phase shift can also becalculated between the waveform of both the intracranial pressure andblood pressure waveforms which also serve as an index of intracranialpressure, intracranial compliance, or another physiological parameter.

Processor 174 can be configured to identify initial waveform featureindices and correlations between these indices can be captured fromvarious sensor modalities after implantation in a patient. Processor 174can also be configured to compare current real-time waveform features toan initial set of reference calibration features established for thevarious sensor modalities enables the detection of either aphysiological condition or an improper calibration of the ICP monitoringdevice.

A library of patient waveform data acquired from multiple patients andtime points across a number of sensor modalities can be stored innon-transient computer storage 176. At block 2008, the measuredwaveforms are compared to waveforms in a waveform library stored innon-transient computer storage 176. Processor 174 determines whetherthere has been a change in a physiological condition of a patient,sensor baseline drift, or improper calibration of a sensor through thiscomparison. For example, if a difference between current real-timewaveform and an ICP value stored in non-transient computer storage 176corresponding to a same position is above a threshold value, then anerror signal is generated notifying a patient or caretaker of a problemthat there is a problem with the sensor. If a difference between thecurrent real-time waveform and an ICP value stored in non-transientcomputer storage 176 corresponding to a same position is below athreshold value, then the data can be stored by ICP monitoring device100 and/or transmitted to an external device 200, 300, 400, 500 fordisplaying the ICP measurement to a user.

Processor 174 is also configured to correlate measured pressures tochanges in non-invasive measurements. Such measurements include, but arenot limited to, carotid artery pressure waveforms, peripheral arterypressure waveforms, tonometry, MRI scanning algorithms, acousticemissions, visual evoked potentials, transracial Dopplers, ultrasonicresonance, and skull pulsations. In one example, carotid artery pressureand peripheral artery pressure waveforms are used to analyze impedancechanges in the carotid waveform attributable to intracranial impedance.

Other features such as the time delay between features, such as thesystolic maximum and the dicrotic notch of a blood pressure waveform,are used by processor 174 to characterize intracranial impedance whichcan be correlated to measured pressure to determine actual pressure.Processor 174 is also configured to correlate or calibrate measuredpressure against an invasive measurement of pressure such as pressuremeasured through a lumbar drain, an omaya reservoir, a ventricularcatheter, cerebrospinal fluid shunt, or a vascular catheter in a vein orartery.

In some embodiments, processor 174 is configured to analyze a number ofwaveform features to provide information regarding the condition of thepatient. Such conditions include, but are not limited to, a change inintracranial pressure, intracranial compliance, oxygenation, heart rate,temperature, respiratory rate, carotid pressure waveform, peripheralartery waveform, or in cerebral perfusion pressure. Algorithms utilizinga number of the waveform features or relations are stored innon-transient computer storage 176 for execution by processor 174. Insome embodiments, the algorithms executed by processor 174 are used forthe prediction of rises in ICP, diagnosis of acute stroke, tool forimproved accuracy in diagnosis of normal pressure hydrocephalus, orassessing the responsiveness to a treatment aimed at changingintracranial compliance. Algorithms can include a number of mathematicalfunctions or experimentally validated relationships, heuristicalgorithms, transfer functions, statistical models, or deterministicmodels.

The waveform analyses described above may be performed by a processorseparate from processor 174 after the data acquired by ICP monitoringdevice 100 is transmitted to an external unit. For example, theelectronics of ICP monitoring device 100 are configured to permitbidirectional transmission of data such that data may be received fromand transmitted to an external device.

In some embodiments, for example, data is transmitted from ICPmonitoring device 100 to a separate device via an inductive couplinglink. Data is sent by modulating a property of a resonant circuit, whichmay be coupled to or included in communication module 178 and/or antenna180, in such a way so as to induce a detectable current change on theother end of the inductive coupling link. The modulation may be suchthat data transmitted is frequency shifted, phase shifted, etc. Thecircuitry connected to the resonant circuit is designed to filter outthe carrier frequency at which the inductive coupling resonates, leavingjust the data waveform, which may be decoded by digital electronics andinterpreted in embedded software as will be understood by one ofordinary skill in the art.

In some embodiments, antenna 180 may be a separate antenna frominductive coupling link, which, when matched with appropriate circuitry,enables ICP monitoring device 100 to transmit data as will be understoodby one of ordinary skill in the art.

An external unit can send commands over the inductive coupling link orseparate antenna to the implanted electronics to program or select inwhich of several modes the processor 174 is to operate. Examples of suchoperating states include, but are not limited to, reprogramming,calibrating, streaming data for a predetermined amount of time, andlong-term standalone operation.

A long-term, standalone monitoring operation is an operation in whichthe external device or unit is to be removed and ICP monitoring device100 continues to record or sense ICP data. In such an operating mode,the circuit elements disposed on PCB 114 operate in a state of minimalpower draw, which uses a low-power timing circuit to alternate betweenpowering off and powering on some subset of the modules in theelectronics. For example, processor 174 may periodically receive sensedsignals from strain gauges 146 and store the data in storage 176. Whennot acquiring data, processor 174 may turn off one or more of gyroscope182, accelerometer 184, communication module 178, ADC, on-boardelectronic components including electronic timers or clock modules, andother integrated circuits as will be understood by one of ordinary skillin the art. The recorded data can be transmitted to an external unit inresponse to receiving a trigger signal from the external unit or at apreprogrammed time.

FIG. 14 illustrates one example of a hand-held device 200 configured totransmit and receive data and control signals from ICP monitoring device100. Hand-held device 200 includes a housing 202 comprising atransmission end 204 and a handle 206 disposed opposite and coupled totransmission end 204.

Handle 206 of housing 202 can be at least partially hollow such that areplaceable or rechargeable power supply can be stored therein. Forexample, replaceable or rechargeable batteries can be stored in handle206 of housing 202 for powering a communication unit disposed within204. Rechargeable batteries can be recharged by plugging the hand-heldunit into a wall outlet via a micro-USB or other physical interface suchas a holster that includes metal charging prongs.

In addition to housing transmission circuitry, transmission end 204 ofdevice 200 can include a speaker and/or one or more light emittingdiodes (“LED”) for providing an audible and/or visual notification to auser that identifies when data is successfully transmitted to orreceived from ICP monitoring device 100. For example, a single beep maybe emitted from a speaker when data is successfully read from and/ortransmitted to ICP monitoring device 100, and multiple beeps may beemitted from the speaker when there is an error transmitting orreceiving data. Similarly, a green LED may light up when data iscorrectly transmitted, and a red LED may light up when data an erroroccurs during transmission.

Additionally, during implantation of the ICP monitoring device 100,device 200 may emit an audible beer or turn on a colored LED to informthe user that the ICP monitoring device 100 has been properly implanted,which may be determined by the ICP monitoring device 100 transmitting anacceptable ICP waveform and/or determining when physical contact hasbeen made with the dura matter, pia matter, or parenchyma. Other methodsof providing user feedback, such as a device for vibrating hand-helddevice 200, may be disposed within and supported by housing 202.

FIGS. 14, 15, and 16 illustrate other possible implementations ofexternal devices 300, 400, 500 that may be used in connection with ICPmonitoring device 100. Referring first to FIG. 15, ICP monitoring device100 is coupled to an external device 300 by a wire 302. External device300 is configured as an ear piece and is sized and configured to be atleast partially received in the ear concha or canal.

In the embodiment illustrated in FIG. 16, external unit 400 isconfigured as an ear piece that is configured to fit behind a patient'sear. Unit 400 is coupled to ICP monitoring device 100 via wire 402,which may include a resonant circuit and coil for inductive couplingwith coil 188 disposed on PCB 114. In the embodiment illustrated in FIG.17, external unit 500 is placed directly on the scalp overlying the ICPmonitoring device 100. External unit 500 can be secured down with anadhesive or an anchoring stitch.

One of ordinary skill in the art will understand that external devicesmay take other forms or configurations. For example, an external unitcan be integrated into a headband that fits circumferentially around thehead. In such an embodiment, the headband can include or more inductivecoils such that the orientation of the headband is not crucial to thetransmission of power to the implanted ICP monitoring device 100. Otherhead-worn embodiments include hats. The external device can also beimplemented as another worn garment such as a necklace.

In some embodiments, a smartphone or computer peripheral may also beconfigured as an external device, with an inductive coupling link (i.e.,a near-field communication (“NFC”) coil) or a 2.4 GHz transceiver (i.e.,a Bluetooth transceiver or chip) built-in for powering and/orcommunicating with the ICP monitoring device 100. In some embodiments,the external device need not be constantly inductively coupled to theICP monitoring device 100. If the ICP monitoring device 100 is placed ina stand-alone mode as described above, the external device may eitherreceive data periodically when the patient or primary caregiver placesit within inductive coupling range, or may receive data more frequentlyvia a longer-range communication protocol such as one implemented in the2.4 GHz ISM band with a separate antenna 180.

Regardless of the implementation of the external unit 200, 300, 400,500, such unit may be used in an outpatient setting. As such, theexternal unit is designed to be rugged and user-friendly, includingpre-programmable alarms associated with parameters such as mean ICP,sensor baseline drift, and device failure. In some embodiments, theexternal units 200, 300, 400, 500 are configured to record symptomsexperienced by a patient including, but not limited to, faintness, aheadache, a ringing in the ears, etc. The external units 200, 300, 400,500 are configured to store these time-stamped symptoms alongside theICP data that were made at the time of the symptom recording in anon-volatile computer storage.

The acquired data can be transmitted in real-time or at a later time toother devices as described in greater detail below. In embodiments inwhich external units 200, 300, 400, 500 are configured with a display,the external units 200, 300, 400, 500 can display the acquired data, thesymptom onset time, and, optionally, the description overlaid on thegraph of ICP recordings or derived parameters. Such functionalityadvantageously allows primary caregivers to correlate the onset ofsymptoms with certain ICP waveform characteristics, such as an increasein mean ICP.

As illustrated in FIG. 18, the external unit(s) 200 are capable oftransmitting data over network(s) 700 such as, for example, a local areanetwork (“LAN”), a wide area network (“WAN”), the Internet, an EDGEnetwork, 3G, 4G LTE, or other network over which data can betransmitted. Although only external unit 200 is illustrated in FIG. 18,each of the external units 300, 400, 500 as well as other embodimentsthat will be apparent to one skilled in the art may be deployed in thesystem illustrated in FIG. 18 and have the properties and functionalitydescribed with reference to hand-held device 200.

In some embodiments, device 200 is configured to receive data from ICPmonitoring device 100, as described above, and transmit the data to oneor more servers 702 via network 700. For example, device 200 receivesdata from ICP monitoring device 100 and transmits data to server 702 vianetwork 700 or by first transmitting the data to a computer 704-1, whichthen transmits the data to server 702. The transmission of data fromhand-held device 200 to computer 704-1 can be made via a wirelessconnection, via a wired connection using a USB connection or othertethered connection, or via an exchange of a memory device such as an SDcard or other transferrable memory device.

Various types of data can be stored on server 702, which may alsoperform data processing functions. In some embodiments, for example, ICPmonitoring device 100 transmits raw data (i.e., unprocessed oruncorrelated data) to server 702 via an external device 200, 300, 400,500. Server 702, which is configured with one or more processors, storesthe data in a computer readable storage and performs data processingincluding the identification one or more waveform features to provideinformation regarding the condition of the patient. Such conditionsinclude, but are not limited to, a change in intracranial pressure,intracranial compliance, oxygenation, heart rate, temperature,respiratory rate, carotid pressure waveform, peripheral artery waveform,or in cerebral perfusion pressure. As described above, the waveforms canbe used to predict rises in ICP, diagnose acute stroke, improve theaccuracy in the diagnosis of normal pressure hydrocephalus, and/orassess the responsiveness to a treatment aimed at changing intracranialcompliance.

Server 702 is configured to be accessed by primary caregivers and/ordevice technicians to gauge both the status of patients with implantsand the status of the implants themselves. Access to server 702 is madevia network 702 from one or more computers 704-1, 704-2, . . . , 704-n(“computers 704”), from a personal digital assistant (“PDA”) 706, from asmartphone 708, and/or other device capable of accessing network 700 viaa browser or other connection interface. Other examples ofnetwork-enabled devices that can access server 702 via network 700include, but are not limited to, portable music players having Wi-Ficapabilities, tablets, televisions, and Blu-ray players to name a fewother possibilities. The network access to server 702 is facilitated bya secure web interface via browser located on the network-enableddevice.

The network-enabled devices, e.g., computers 704, PDA 706, phone 708,etc., can be configured to function as a patient monitoring device. Forexample, server 702 can transmit alarms and/or status updates vianetwork 700 to one or more of the network-enabled devices 704, 706, 708.Such alarms and/or status updates can be transmitted using emails, textmessages, automated phone calls, or other communication methods thatwill be apparent to one of ordinary skill in the art. The status updatesand/or alarms can be displayed on a display or trigger an audio alert onthe network-enabled devices 704, 706, 708 that function as a patientmonitor. As will be understood by one of ordinary skill in the art, thenetwork-enabled devices 704, 706, 708 can reside with the patient, thepatient's caregiver, and/or a physician whom the patient might see in anoutpatient clinic, urgent care center, or emergency room.

In some embodiments, network-enabled devices 704, 706, 708 that functionas patient monitors are capable uploading data to and downloading datafrom server 702. Examples of data that can be transmitted from anetwork-enabled device includes, but are not limited to, a patient'sphysiological parameters, the number and identity of ICP monitoringdevices 100 being monitored by the network-enabled device 704, 706, 708,and the software version running on the unit and/or the ICP monitoringunit 100. Additionally, network-enabled devices 704, 706, 708 areconfigured to download software upgrades and historical data related toa patient's physiological parameters from server 702. Network-enableddevices 704, 706, 708 are also configured to optionally store datareceived from ICP monitoring unit 100 via external device 200, 300, 400,500 and/or server 702 internally, or to transmit the downloaded data ordata derived from the downloaded data to ICP monitoring unit 100 orserver 702.

Network-enabled devices 704, 706, 708 are configured with a processorcapable of processing data received from ICP monitoring device 100 viaan external unit 200, 300, 400, 500, data received from server 702, orsome combination thereof, in certain ways to determine certainparameters for display to a user. These parameters may include anestimation of baseline sensor drift, mean ICP, ICP pulsatility, andother parameters. Devices 704, 706, 708 can display the parameters onthe display of the device as a chart, numbers, graphs, annotationsoverlaid on graphs, or other visual presentation.

As will be understood by one of ordinary skill in the art,network-enabled devices 704, 706, 708 are configured with a user inputdevice, such as a keyboard, a touchscreen for displaying a virtualkeyboard, a microphone for receiving audio instructions, camera, orother interface for receiving data from a user. A user can use the userinput device to set one or more alarm thresholds related to certainphysiological parameters, send commands to an external unit 200, 300,400, 500 and/or an ICP monitoring device 100, create annotations to beoverlaid on graphs of certain physiological parameters, to name a fewnon-limiting possibilities.

The disclosed devices, methods, and systems advantageously enable theICP of a patient to be monitored with improved accuracy and withimproved intelligence. The incorporation of an accelerometer and/orgyroscope in an ICP monitoring device advantageously enables the ICPmonitoring device to determine position-related events such as sleeping,falling, and running, to name a few possibilities. The detection of suchposition-related events can trigger alerts to caregivers and enablesimproved diagnostics to be performed on recorded data. For example, theICP monitoring device can be used to acquire diagnostic measurements fornormal pressure hydrocephalus when it is determined that a patient issleeping.

Waveforms generated from acquired or sensed data can be used to deriveactual physiological measurements including, but not limited to,pressure, tissue compliance, or oxygenation. Given that measurement ofwaveform features is independent of sensor baseline drift, pressuremeasurement may be achieved without having to extract the sensor forexternal calibration or use an externally connected pressure reference.Moreover, having a calculated pressure derived from feature basedanalysis is beneficial in calibration and correction of an actualmeasured value. The difference between the derived value of pressure orother physiological parameter and the actual measured value can becalculated and the sensor can alert the user if the difference exceeds aspecified error threshold, signaling that recalibration may benecessary.

The present devices, systems, and methods can be embodied in the form ofmethods and apparatus for practicing those methods. The present devices,systems, and methods can also be embodied in the form of program codeembodied in a non-transient, tangible media, such as USB flash drives,memory cards, CD-ROMs, DVD-ROMs, Blu-ray disks, hard drives, or anyother non-transient machine-readable storage medium, wherein, when theprogram code is loaded into and executed by a machine, such as acomputer, the machine becomes an apparatus for practicing the invention.The present devices, systems, and methods can also be embodied, at leastpartially, in the form of program code, for example, whether stored in astorage medium, loaded into and/or executed by a machine, or transmittedover some transmission medium, such as over electrical wiring orcabling, through fiber optics, or via electromagnetic radiation,wherein, when the program code is loaded into and executed by a machine,such as a computer, the machine becomes an apparatus for practicing theinvention. When implemented on a general-purpose processor, the programcode segments combine with the processor to provide a unique device thatoperates analogously to specific logic circuits.

Although the devices, systems, and methods have been described in termsof exemplary embodiments, they are not limited thereto. Rather, theappended claims should be construed broadly, to include other variantsand embodiments of the devices, systems, and methods, which may be madeby those skilled in the art without departing from the scope and rangeof equivalents of the devices, systems, and methods.

1-20. (canceled)
 21. A device for generating data related tointracranial pressure (ICP), comprising: a housing; a first sensorconfigured to generate signals indicative of the ICP; a second sensorconfigured to generate signals indicative of an orientation of the ICPdevice; and circuitry coupled to the first and second sensors andconfigured to: generate ICP data based on the signals indicative of theICP, generate orientation data based on the signals indicative of theorientation of the ICP device; and associate the ICP data with theorientation data for determining the ICP.
 22. The device of claim 21,wherein the circuitry is further configured to determine the ICP basedon the association of the ICP data with the orientation data.
 23. Thedevice of claim 21, wherein the circuitry is configured to transmit theICP data and the orientation data to a separate device for determiningthe ICP.
 24. The device of claim 21, wherein the circuitry is furtherconfigured to store the ICP data and the orientation data in a computerreadable storage.
 25. The device of claim 21, wherein the circuitry isfurther configured to determine one or more position-related events. 26.The device of claim 25, wherein the one or more position-related eventsis lying down, sleeping, falling, or running.
 27. The device of claim21, wherein the first sensor comprises a diaphragm configured to deformin response to the ICP.
 28. The device of claim 27, wherein the firstsensor further comprises a strain gauge configured to detect deformationof the diaphragm.
 29. The device of claim 28, wherein the strain gaugecomprises: first and second strain gauges aligned with each other anddisposed adjacent to a radial center of the diaphragm, and third andfourth strain gauges aligned with each other and perpendicular to thefirst and second strain gauges, the third strain gauge disposed betweena side wall of the housing and the first strain gauge, and the fourthstrain gauge disposed between the side wall and the second strain gauge.30. The device of claim 29, wherein the first, second, third, and fourthstrain gauges are electrically connected in a Wheatstone bridge.
 31. Thedevice of claim 27, wherein the diaphragm defines a bottom wall of thehousing.
 32. The device of claim 31, the housing further comprising asidewall and a ridge, the ridge forming on interface between the bottomwall and the sidewall.
 33. The device of claim 32, wherein the firstsensor further comprises a strain gauge configured to detect deformationof the diaphragm, the strain gauge located along an axis of neutralityof the diaphragm.
 34. The device of claim 21, wherein the second sensoris configured to generate signals indicative of an orientation of theICP device relative to a vertical direction.
 35. The device of claim 21,wherein the second sensor is an accelerometer.
 36. The device of claim21, wherein the second sensor is a gyroscope.
 37. The device of claim21, wherein the second sensor and the circuitry are disposed on aprinted circuit board.
 38. The device of claim 21, wherein the housingincludes a proximal portion and a distal portion such that, in use, thedistal portion is received within a hole of a patient's head and theproximal portion is located outside the hole.
 39. The device of claim21, wherein the first and second sensors are configured to generate therespective signals for a period of time and the circuitry is furtherconfigured to associate the ICP data with the orientation data for theperiod of time.
 40. The device of claim 22, wherein the first and secondsensors are configured to generate the respective signals for a periodof time and wherein, to determine the ICP based on the association ofthe ICP data with the orientation data, the circuitry is furtherconfigured to generate a pressure waveform for the period of time.
 41. Adevice for generating data related to intracranial pressure (ICP),comprising: a first sensor; a second sensor; and circuitry configuredto: receive signals from the first and second sensors; generate ICP databased on the signals from the first sensor; generate orientation databased on the signals from the second sensor; and associate the ICP datawith the orientation data for determining the ICP.
 42. The device ofclaim 41, wherein the circuitry is further configured to determine theICP based on the association of the ICP data with the orientation data.